Construction machines having hydraulically controlled implements often include one or more variable displacement hydraulic pumps that are driven by an internal combustion engine. As the operator manipulates the implements through levers or other input devices in the operator cabin, the hydraulic system responds by directing hydraulic fluid flow to appropriate hydraulic circuits. To move an implement carrying a load in a desired direction at a desired velocity, the operator may operate one or more levers that direct flow of a hydraulic fluid, to apply force, and move the implement. As the operator requested hydraulic effort increases, the hydraulic control system increases the displacement of the variable displacement hydraulic pump such that the amount of hydraulic flow increases. Since the amount of power required to drive the hydraulic pump is a function of pressure and flow, as flow increases, a higher amount of engine power is expended to operate the implement. Load on the engine, is therefore, a function of hydraulic flow and pressure. Under some operating conditions, the amount of hydraulic power exceeds the amount of power the engine is capable of producing at that engine speed. When this occurs, the rotational speed of the engine decreases along its lug curve. This condition is typically referred to as engine lug.
When the engine lugs, operator perception of engine power may be adversely affected. In extreme cases, the engine may even stall if the requested hydraulic power becomes too high. To reduce lug and avoid stalling the engine, the operator may reduce the amount of hydraulic power being requested when they sense a loss of engine speed. While this action avoids engine stall, the operator may overcompensate and reduce the amount of hydraulic work to a greater extent than needed to prevent stall. As a result, machine productivity may be reduced. Fuel combustion in the engine during lug may become less efficient, resulting in increased emissions and reduced fuel economy. As a result, it may also be desirable to reduce engine lug to decrease emissions and fuel consumption. Some level of engine lug, however, may be desirable to operate the machine at maximum capacity. Therefore, the hydraulic system may be controlled to ensure that the machine is working at maximum capacity while limiting emissions and fuel consumption.
U.S. Pat. No. 5,525,043 ('043 patent), issued to Lukich on Jun. 11, 1996 and assigned to the assignee of the current disclosure, describes a hydraulic control system to reduce engine lug. In the control system of the '043 patent, multiple sensors are used to detect various operating parameters of the hydraulic system including the pump and an engine driving the pump. Based on these sensor inputs, a parameter signal that indicates the load on the engine is calculated. When the load on the engine increases above a predefined level, the displacement of the variable displacement pump is reduced to allow the engine speed to increase to the predefined level. In the control system of the '043 patent, the parameter signal is determined based on a number of operating parameters of the hydraulic system to accurately control engine speed with a minimum amount of oscillation (overshoot and undershoot). While quick and accurate control of engine speed by preventing oscillations, as disclosed in the '043 patent, may be important in some applications, it may not be as important in other applications. Although the control system of the '043 patent may effectively control engine lug, the complexity of the methodology employed may make the system expensive for some applications. The present disclosure is directed to solving one or more of the problems set forth above and/or other problems in the relevant art.